In the power driven transmission arts, and particularly in the automobile transmission arts, multiple helical gears are typically employed. Since each set of gears meshes differently due to variations within its manufacturing tolerances, and since an axial thrust is exerted by rotation of the gears, thrust bearings are required to carry the axial thrust load. Because of the manufacturing tolerances, the axial dimension required of the thrust bearing may vary; considerable variation may result if multiple gears are employed on a single shaft. In the prior art, shims or spacers of varying axial dimension have been used to take up or fill this variable axial dimension.
During assembly, the gears are selected and installed, leaving an axial dimension or space to be filled by the thrust washer and spacer. This space must be carefully measured. A thrust bearing is first selected, and then a spacer of the desired axial dimension must be selected and located from among the available supply of washers. The spacer and thrust bearing combination must preceisely fill the axial dimension. Often, a plurality of spacers are tried and tested until the right spacer or combination of spacers properly fills the available axial space. This is a difficult and time-consuming task requiring patience and careful attention to detail.
In practice, the gear train is assembled in a transmission on a conventional assembly line. For manufacturing convenience, the transmissions are typically carried by overhead suspension conveyors, and at least some of the parts, including the thrust bearing and spacer, are assembled by inserting these lighter weight bearing parts upwardly into the interior of the suspended transmission from which the shaft extends downwardly. Thrust washers and selected spacers are typically assembled and joined by a thick grease-like compound before being inserted upwards into the suspended transmission and onto the shaft. The grease compound is the primary means for securing the combination onto the exposed, downwardly extending shaft during assembly. The sticky, grease-like compound, however, is prone to picking up undesired environmental dirt and contaminants.
U.S. Pat. Nos. 4,725,153 and 4,733,479 to Tsuruki teach the use of variable axial dimension spacers or shims which snap in place on the thrust bearing portion. In some embodiments disclosed in the Tsuruki patents, annular shims having inner or outer dimensions permitting an interference fit ("interference margin") with internal or external flanged portions of the bearing cage are disclosed. The bearing cage flanges are dimpled or deformed so as to reduce the tolerance of the fit to less than zero clearance in order to require forcible mounting of the shim to the bearing assembly. The manufacturing tolerance of such interference-fit piece parts can be difficult and expensive to maintain, leading to undesirable costs or difficulties during assembly
Another shim disclosed by Tsuruki includes a series of dimpled peripheral flanges having interference fit dimensions which snap over the bearing periphery. In addition to the previously mentioned problem with interference fit manufacturing tolerances, this alternative shim is formed of a single piece of material having uniform thickness, and thus the dimpled peripheral flange portions are necessarily of the same thickness as the shim. The external diametrical dimensions of a thrust bearing/spacer assembly become intolerably large with thicker spacers and are thus limited, for practical purposes, to thin shims.
In addition, difficulties in marking the axial dimension on prior art spacers while maintaining the dimensional tolerance thereof present unwieldy sorting problems for assembly line workers.